The Perl Advent Calendar needs more articles for 2022. Submit your idea today!



                 .---------.  .---------.
                 | State 1 |  | State 2 |
                 '---------'  '---------'
                    ^   \         ^  \
                   /     \       /    \
                  /       \     /      \
                 /         \   /        \
                /           \ /          \
               /             v            v
            ******        ******        ******
            * T1 *        * T2 *        * T3 *
            ******        ******        ******
               ^             ^             /
                \             \           /
                 \             \         /
                  \             \       / stimuli
                   \             \     /
                    \             \   v
                     \         .---------.
                      '--------| State 3 |
                               '---------'